Process of manufacturing nitric acid.



UNITED sTATEs PATENT oEE-ioE.

WiL-HELM osTwAvLD, oF LEIPzi'G, GERMANY.

PROCESS OF MANUFACTURING NITRIC ACID.-

Specification of Letters Patent.L

Patented Ju1y 2, 1907.'

Application filed -T une 26, 1902. Serial No, 113,333. l

of which my process may be carried out is represented in a longitudinalsection.

In the drawing a is a tube for supplying the gas mixture, b is a tubeclosed at both-ends, c is a tube of smaller diameter than vb and open atboth ends, said tube passing through one of the 'end walls of the tubeb.

d is a catalytic substance allowing the gas mixtureto pass through andover it, g and h are pumps for supplying the gases, i is a vessel`forcondensing the reaction products.

The action of catalytic agents, or so-called I contact bodies on amixture of ammonia and oxygen, whereby nitric acid or nitrogen oxidscapable of' being converted into nitric acid by the further action ofoxygen are produced` is known as a laboratory reaction. But

it was hitherto impossible to Acarry out this process on a practical ortechnical scale for the reason that the yield in nitrogen oxids from agiven quantity of ammonia was too small. Now I have found rthat bymaintaining during the reaction certain definite conditions it ispossible to convert annnonia into nitric acid or nitrogen oxids, withnearly the theoretical yield.

Oxygen may react onammonia by means of catalytic agents in two differentways which, howeverl may take place simultaneously: (a)." The ammonia isoxidized .should at least Vcorrespond to the following formula:

but it is advisable to use a larger quantity of oxygen. The secondcondition is that the temperature of the gas mixture while in contactwith the catalytic substance is kept at above 300 C. It is preferable tomaintain the temperature between dark and brightred heat.

lSimilar conditions for carrying out thc reaction are.

broadly-*mentioned in chemical text books andl cyclopedias, but suchmention is merely of laboratory interest, and it is not possible fromsuch brief allusions t0 utilize thc reaction in a `practical orvcommercial way for the technical production of nitric acid. Now I havefound that the reason ior this is that while in other catalyticprocesses, such as the formation of sulfur trioxid, the product to beobtained is the final product of the reaction, in this case the nitricacid or nitrogen oxids are not the final products of the reactions. -Ihave stated that two different reactions are involved, namely, the'oxidation of ammonia' to nitric acid and nitrogen oxids, and adecomposition of the nitric acid and nitrogen oxids, free nitrogen beingthus formed` Consequently while in other catalytic reactions the yieldcannot be influenced by 'a' longer contact ofthe reaction products withthe catalytic agent-these products not being injured by prolongedcontact,-n the production of nitric acid and nitrogen oxids a longercontact of these products with the catalytic agent is injurious becauselthese valuablev products are then decomposed and transformed intovalueless nitrogen.

N ow in all experiments hitherto described the speed with which the gasmixture is allowed toi'low over and through the `catalytic agent is notat all mentioned,

and evidently the speed has been that which was usual` 'in similarcatalytic reactions. Now I have found that this speed is too small forobtaining a good yield I formation of nitrogen, and by this fact thethird coni dition for practically carrying out the oxidation of ammoniato nitric acid or nitrogen oxids is fixed. Indeed, for obtaining goodresults it is necessary to allow the gases to flow through and over thecatalytic agents with a speed never used hitherto in such reactions andto use therefore as short or thin layer of catalytic 'substances aspractically possible'. lThe only requirement is that the speed 'must notbe so much increased that portions of the ammonia pass through thecatalytic dently the speed will depend in every special case onthenature, the surface and the distribution ofthe contact bodies orcatalytic agents and must therefore be determined by experiment. In thisexperiment the speed is increased until-unoxidized ammonia can be testedin the reaction products and the speed is then kept a little below thislimit, but as near to this limit 'as it may be. practically pos-sible.In other words,

the velocity should be such that, increased, unoxidized ammonia wouldbefound in the product.

When usingpa catalytic agent composed of solid 'platinum andplatinum-black, as will be further on described, it has been foundadvantageous to allow the gases to be in contact with the catalytic`agent for about one-hundredth of a second. It is, however, evident thatin practically carrying out the process it is not possible to maintainthe speed of the gases absolutely constant, and there will be certainvariationsof 4the /speed. Now thesevariations present certain diffiandweight it'might be cooled down so much as not to be longer able tomaintain the reaction. For overcoming these difficulties I heatthe gasmixture to be oxidized by meansl of the hot reaction products in such away thatfwhen the gases flow slowly, more heat is transferred to themfrom the reaction products, and vice versa. For carrying this intopractice, I supply lthe gases in any suitable manner, for instance, asrepresented in the drawing, by supplying oxygen or air by means of apump g and ammonia by means of a pump h in such quantities as correspondto .the first conditionabove indicated land mixing these gases in thetube a. I then allow the mixturef-to-'flow through the tube b along thewallsof the tube c, then to pass through and over the catalytic orcontact body d, lthence through thetube c, and I then conduct the` 35'gases to a condensing device i known manner.

If the catalytic agent is sufficiently heated at the constructed in. any

vbeginning of the operation, and if the speed of the gases. has beenregulated for a particular gas mixture and particular catalytic agentesabove set forth, the

ammonia isoxidized when coming into contact with the catalytic agents.The hot products flow through the tube c and the reaction products arecondensed in the vessel i. The hot products of reaction will then heatthe gases flowing through the tube b, and thus the mixture is heatedwhen it comes into contact with, the catalytic agent. Now, if the speedof the gases is lessf ened by any reason, if the gas mixture would cometo the catalytic agent with the same temperature as before, thiscatalytic agent would be cooled as not so much reaction heat would beevolved in the unit of time. The efficiency of the catalytic agent wouldthen be diminished and the reaction might even be entirely stopped. Now,by the arrangement justdescribed, in such a case the gas mixture, beforecoming to the catalytic agent, is he. ed to a more elevated temperaturethan before,

`as it is in longer contact with the walls of the tube c,

and more heat is transferred from the hot reaction ,products to the gasmixture `flowing through the tube b. `In consequence the gas mixture,when arriving' at the catalytic agent is heated .to a more elevatedtemperaf ture than before and the catalytic agent is therefore the speedof the gases is increased,.not so much heat is' preventedfronrbeingcooled. On .the other hand, if

qalytic agent should not be allowed transferred from the reactionproducts through the walls of the tube c to the gas mixture flowingthrough the tube b and the mixture arrives to the catalytic agent with alower temperature than before, the catalytic agent being thus preventedfrom being overheated. By the heat interchange relation thus provided,the temperature of the catalytic agent is automatically regulated andmaintained at the temperature which has been found suitable at thebeginning of the operation. No special heating device for the gasmixture is necessary. The initial heating of the catalytic substance maybe effected in any suitable way. For instance a. flame may be directedtowards the contact-body till the regular reaction of thc process heatsit automatically. The contact-body may if dei sired be heated by anelectrical heating arrangement.

In carrying out this process I use for instance the following materialsfor making thecontactbodies: Me tallic platinum in asolid state,metallic palladium, iridium, rhodium, the oxids, especially the higheroxids, of manganese, lead, silver, copper, chromium,

' nickel, cobalt, vanadium, molybdenum. A catalytic agent made of solidplatinum in combination with platinuni in a state of very finesubdivision, such as platinum sponge or the like has been found the mostadvantageous. .i It has been found that metallic platinum with acontinuous smooth surfacev effects at red heat the conversion of theammonia into nitric acid at a moderate velocity of the reaction, whileit causes the second reaction mentioned above, viz. the generation offree nitrogen only after a rather long time of contact.

The platinum in a state of very Ifine division on the otherhand causesan acceleration of both possible reactions, but a greater one of thesecond reaction. Thus if it be employed alone in the process, it willgenerate nitrogen besides the oxids of nitrogen; By combining both` thematerials, the solid continuous and the finely divided platinum, in suchproportions that the second reaction is insignificant the generation ofnitric acid is considerably accelerated.

For preparing the described catalytic agent composed of compact andfinely divided platinum, I coat compact platinum with al paste ofammonium platinum chlorid and water, and treat the paste at a suitabletemperature sufficient for transforming the ammonium platinunijchloridinto porous platinum. The distribution of tlfe paste, and therefore ofthe nely divided platinum may be determined by the competent ,workman byway of experiment for any required case. l

The arrangement of the catalytic agent for thisprocess may be various.Generally a length'of one-to two centimeters of platinum is Asuiicient,when the gas mixtureflows with aspe d of 1 to 5 meters per second. Ifthe gas is passing wit a lower speed a shorter length oi platinum may beused and vice versa. The catalytic agent for example be made ofribbonsof platinumplates placed side by side ,the plates being alternately Yplane and grooved, undulated, or made uneven in any way. By thisarrangement pipe-like channels, lying side by side, are presented tothepassing gas mixture. Another arrangement ofthe catalytic agent is toplace ribbons of platinum plates, alternately longitudinally andVtransversely'grooved, one 'upon another, or generally to combine severalof these ribbons, made uneven 'in the same way, with ribbons made unevenin any other way. Farther on, the catalytic agent may be made oi a wirenet, or oi a perforated plate through the openings of which the gasesare driven. If necessary it may be made of several such plates oneplaced behind the other.' Moreover suitably shaped bodies ofa materialoffering resistance,` for instance porcelain, may be coated withplatinum by ay mechanical, an electrical, or a chemical process and suchbodies may be arranged as layers of a suitable thickness. Finally smallturnings, chips, or balls of wire, or any other suitable masses of anyshape having a great surface and forming permeable plates or the like,may be usedor this purpose. Thespecial form will be chosen by thecompetent workman according to the convenience of the special case.

For carrying the invention into practice it has furthermore been foundadvantageous to make the mixture of airand ammonia gas in a specialmanner. In this process gas mixtures containing but ,little ammonia mayhe used with success. Therefore, the mixture of ammonia and air may beproduced in tire following way. Gaswater, putrid urine, or other liquidscontaining ammonia are treated, according to the-principle of thecounter current, with air, after 'being mixed, ii' necessary, with limeor another strong alkali for the purpose of decomposing the salts ofammonia. The ammonia is thus taken up by the air. By treating theliquids in such a manner that fresh air comes in Contact with a nearlyexhausted liquid, and the air rich in ammonia goes through the freshliquid, there will thus be secured a nearly complete utilization of theammonia with a minimum of air.

The proportions of ammonia to air in this process may be much less than`l/lO without seriously injuring the production of nitric acid.Therefore the utilization oi the diluted ammonical liquids may beeffected at ordinary temperature v'or with very little heat. By emoploying heat in this lprocess also very dilute liquids may beutilzedwhich would scarcely permit any other technical utilization. The heatcreated by the production of nitric acid may also be used for drivingout the` ammonia from these liquids. i v

` What I claim is:

1. The herein described process of manufacturing nitric acid andnitrogen oxids, which consists in conducting a mixture of ammonia andoxygen bearing gases in substantially the proportions specified over acatalytic agent at a speed such that, if increased, unoxidized ammoniawill appear in the reaction products.

2. The herein described process of manufacturing nitric acid andnitrogen oxids, which consists in conducting a mixture of ammonia andoxygen bearing gases in substantially the proportions specified over acatalytic agent, and owing the reaction products in heat interchangingrelation with the mixed gases passing to the catalytic agent, wherebythe catalytic agent is maintained at the suitable temperature for thereaction irrespective of variations in the speed of flow of the gases.

3. The hereinbefore described process of manufacturing nitric 'acid andnitrogen oxids which consists in conducting a mixture of ammonia andgases containing oxygen in the proportion of at least seven atoms ofoxygen to two molecules of ammonia at a temperature exceeding 300 C,over and through a catalytic agent with a 'speed approached as much aspractically possible to the limit beyond which unoxidized ammonia isfound in the escaping gases, and condensing the oxidation products.,v

4. The herelnbefore described process ofmanufacturing nitric acid andnitrogen oxids which consists in conducting a mixture of ammonia andgases containing an excess of oxygen in the proportion of at least sevenatoms of oxygen to two molecules ot' ammonia at a temperature exceeding300c C. over and through a catalytic agent with a speed approached asmuch as practically possible to the limit beyond which unoxidizedammonia is' found in the escaping gases, conductiiig'the reactionproducts in heat interchanging relation to the gas mixture owing to thecatalytic agent and thereby transferring more heat from the reactionproducts to the gas mixture if the speed is diminished and less heat ifthe speed is increased, and condensing the oxidation products.

In witness whereof I have hereuntosigned my name this 11th day of -Jnne1902, in the presence of two subscribingr

